An electron microscope is an observation device which obtains an enlarged image of a specimen and information of constituent elements by using an electron beam. In the electron microscope, a precise enlarged image of the specimen and an elemental-composition analysis result of the specimen are obtained by an electron beam. For this reason, the role of an electron gun generating an electron beam plays a large role.
It is important for the electron gun to keep the internal residual gas pressure thereof low. To pump residual gas molecules in the electron gun and keep the molecules at low pressure, the electron gun is provided with a vacuum pump such as an ion pump (sputter ion pump). An ion pump is a device that ionizes residual gas molecules in a vacuum container by collision with an electron beam and pumps residual gas by the occlusion of the gas in an inner wall.
Furthermore, in recent years, a non-evaporable getter (NEG) pump suitable for pumping residual hydrogen molecules has been used in combination with an ion pump. PTL 1 discloses an electron gun provided with an ion pump and an NEG. Furthermore, PTL 2 discloses an electron gun provided with an NEG around an electron source.